This invention relates to an improved process for removing sulfur dioxide (SO.sub.2) from mixtures, especially dilute gaseous mixtures containing less than 1% sulfur.
Many processes are known for the removal of sulfur dioxide from mixtures. These processes include SO.sub.2 removal from dilute flue gas mixtures such as those produced by power utilities as a by-product from burning sulfur-containing coal or oil. Known processes take a variety of approaches including both wet and dry scrubbing as well as catalytic oxidation, adsorption and even in situ reactions with burning fuel. See generally, the Kirk-Othmer Encyclopedia of Chemical Technology, Second Ed., Vol. 19, 415 (J. Wiley and Sons, Inc., 1969).
In the article, L. A. Haas et al, "Removing Sulfur Dioxide by Carbon Monoxide Reduction", Report of Investigations 7483, U.S. Dept. of the Interior, Bureau of Mines (1971), a catalytic process is described which employs an iron-alumina mixture as a catalyst in the reaction of SO.sub.2 with carbon monoxide (CO) to produce carbon dioxide and elemental sulfur. This article further states that only small quantities (less than 0.5%) of oxygen can be tolerated without impairing the reaction.
U.S. Pat. No. 4,238,466 describes a process for removing sulfur dioxide from a gas which contains oxygen by contacting the gas with a ferrous sulfate sorbent at a temperature between 300.degree.-500.degree. C. with an O.sub.2 /SO.sub.2 ratio of about 1.
Several patents describe the use of iron oxide as a sorbent to remove sulfur dioxide from mixtures containing both sulfur dioxide and oxygen. See, e.g., U.S. Pat. Nos. 3,917,800; 4,008,169; and 4,010,239. There is, however, a continuing need to develop better methods of removing SO.sub.2 from mixtures, in particular, dilute flue gases. Such improved methods may promote the societal goals of reducing environmental pollution, economic recovery of waste by-products, and efficient use of raw materials, through cheaper, simpler, and more effective processes.